The invention relates to an enzyme which catalyzes a hydrolytic conversion between soporific fatty acid primary amides and their corresponding fatty acids and is designated a fatty-acid amide hydrolase (FAAH), to methods for enzymatically catalyzing such conversions, and to methods for inhibiting the enzymatic catalysis of such conversions. More particularly, the invention relates to FAAH protein, in either isolated or recombinant form, and to its use and inhibition.
Sleep is a natural, periodic behavioral state during which the body rests itself and its physiological powers are restored. It is characterized by a loss of reactivity to the environment. During sleep, certain physiological processes of both the body and the brain function differently than they do during alert wakefulness. Normal sleep consists of at least two quite different behavioral states: synchronized sleep, during which the electroencephalogram consists of slow waves of high amplitude, and desynchronized sleep (DS) or activated sleep characterized by rapid eye movements (REM sleep), in which the electroencephalogram pattern is characterized by waves of high frequency and low amplitude. Synchronized sleep is further characterized by slow and regular respiration, by relatively constant heart rate and blood pressure, and by a predominance of delta waves. Synchronized sleep usually consists of four stages, followed by a period of activated sleep. Each cycle lasts between 80 and 120 minutes. In contrast, desynchronized sleep is further characterized by irregular heart rate and respiration, periods of involuntary muscular jerks and movements, and a higher threshold for arousal. Periods of desynchronized sleep last from 5-20 minutes and occur at about 90 minute intervals during a normal night""s sleep.
Sleep disorders include sleep deprivation and paroxysmal sleep, i.e., narcolepsy. There has been no known pharmacological method for promoting or inhibiting the initiation of sleep or for maintaining the sleeping or waking state.
Cerebrospinal fluid (liquor cerebrosinalis) is a clear, colorless fluid that circulates within the four ventricles of the brain and the subarachnoid spaces surrounding the brain and spinal cord. Cerebrospinal fluid originates as an ultrafiltrate of the blood secreted by the choroid plexus in the lateral third and fourth ventricles. Cerebrospinal fluid is also sometimes called neurolymph. After passing through the four ventricles and the subarachnoid spaces, cerebrospinal fluid is largely resorbed into the venous system via the arachnoid villi. Cerebrospinal fluid serves as a medium for the removal of catabolites, excretions, and waste materials from the tissues bathed by it. To date, no factor derived from cerebrospinal fluid has been reported to correlate with sleep deprivation. What is needed is a method for analyzing cerebrospinal fluid for identifying a biochemical factor generated by subject that correlates with sleep deprivation.
Since the seminal discovery of prostaglandins, there has been increasing recognition of the role of fatty acids and their derivatives in important physiological processes, e.g., B. Samuelsson, Les Prix Nobel 1982, pp. 153-174.
Cis-9,10-Octadecenoamide has been isolated from the cerebrospinal fluid of sleep-deprived cats and has been shown to exhibit sleep-inducing properties when injected into rats. Other fatty acid primary amides in addition to cis-9,10-octadecenoamide were identified as natural constituents of the cerebrospinal fluid of cat, rat, and man, indicating that these compounds compose a distinct family of brain lipids. Together, these results teach that fatty acid primary amides represent a new class of biological signalling molecules that can be employed for inducing subjects to sleep. Preferred fatty acid primary amides include an alkyl chain having an unsaturation and are represented by the following formula: NH2C(O) (CH2)(6 greater than nxe2x89xa611)CHxe2x95x90CH(CH2)(8xe2x89xa7nxe2x89xa65)CH3. Preferred soporific fatty acid primary amides have an unsaturation with a cis configuration within their alkyl chain. In addition to cis-9,10-octadecenoamide, other soporifically active fatty acid primary amides include cis-8,9-octadecenoamide, cis-11,12-octadecenoamide, and cis-13,14-docosenoamide.
Deutsch et al, Biochem. Pharmacol., 46:791 (1993) has identified an amidase activity which catalyzes both the hydrolysis and synthesis of arachidonylethanolamide (anandamide) from the membrane subcellular fractions taken from neuroblastoma, glioma cells and crude homogenates of rat brain tissues. The study detected the uptake and enzymatic breakdown of arachidonylethanolamide (anandamide) to arachidonic acid (and vice versa) from the homogenates of tissues from brain, liver, kidney and lung but not from rat heart and skeletal muscles.
The active membrane fraction which displayed this amidase activity was prepared by either homogenizing the desired cell line and subsequently subjecting the crude homogenate to density centrifugation or by taking the crude homogenates of rat brains and directly incubating them with anandamide.
The uptake and degradation of arachidonylethanolamide (anandamide) was assayed by incubation of [3H]-anandamide (NEN, NET-1073, 210 Ci/mmol) in the cell culture medium. It was found, by liquid scintillation counting of the aqueous and organic phases, that arachidonic acid and anandamide distributed in the organic phase. Thus, the organic extract of the cell medium was subsequently visualized using thin-layer chromatography, sprayed with a surface autoradiograph enhancer (EN3HANCE, Dupont) and exposed to X-ray film (Kodak X-OMAT AR) at xe2x88x9280xc2x0 C.
The serine protease inhibitor, phenylmethylsulfonyl fluoride at 1.5 mM concentration completely inhibited the amidase activity. Other inhibitors tested had little or no effect on the activity and included aprotinin, benzamidine, leupeptin, chymostatin and pepstatin.
In a second manuscript, Deusch et. al. (J. Biol Chem., 1994, 269, 22937) reports the synthesis of several types of specific inhibitors of anandamide hydrolysis and their ability to inhibit anandamide breakdown in vitro. Four classes of compounds were synthesized and include fatty acyl ethanolamides, xcex1-keto ethanolamides, xcex1-keto ethyl esters and trifluoromethyl ketones. The most effective class of compounds were the trifluoromethyl ketones and xcex1-keto esters. The least potent inhibitors were the xcex1-keto amides and saturated analogs of anandamide.
As an example, when anandamide is incubated with neuroblastoma cells, it is rapidly hydrolyzed to arachidonate but in the presence of the inhibitor arachidonyl trifluoromethyl ketone, there is a 5 fold increase of anandamide levels. The study infers that polar carbonyls such as those found in trifluoromethyl ketones, may form stabilized hydrates that mimic the tetrahedral intermediates formed during the reaction between the nucleophilic residue and the carbonyl group of anandamide. Deutsch suggests that the nucleophilic residue may be the active site of a serine hydroxyl in the hydrolytic enzyme.
This enzyme is classified as an amidase (EC #3.5) where the enzyme acts on carbon nitrogen bonds other than peptide bonds. The amidase activity is inhibited by the serine protease inhibitor, PMSF and the action of trifluoromethyl ketone inhibitors (and others) directly affect the hydrolytic activity of the enzyme. Furthermore, Deutsch suggests that anandamide is cleaved by a mechanism that involves an active site serine hydroxyl group.
What is needed is an identification of enzymes within the brain tissue which catalyze the degradation of soporific compound found in the cerebrospinal, for mediating the soporific activity of these compounds. What is needed is an identification of inhibitors for inhibiting the activity of enzymes which degrade soporific compounds of the type found in cerebrospinal fluid.
An enzyme is disclosed herein which degrades soporific fatty acid primary amides, and is designated fatty-acid amide hydrolase, or FAAH. FAAH is one of the enzymes which mediates the activity of fatty acid primary amides, including soporific fatty acid primary amides.
As disclosed herein, FAAH is characterized by an enzymic activity for catalyzing a conversion cis-9,10-octadecenoamide to oleic acid, among other substrates, as shown in Scheme 1 below, and therefor was originally identified as cis-9,10-octadecenoamidase. However, it is now shown that FAAH has activity to hydrolyse a variety of fatty acid primary amides, and therefore the amidase originally referred to as cis-9,10-octadecenoamidase is more appropriately referred to as FAAH. 
One aspect of the invention is directed to a purified form of FAAH. FAAH can be purified by a variety of methods, including a chromatographic methodology. Preferred chromatographic methodologies include affinity chromatography, electric chromatography, gel filtration chromatography, ion exchange chromatography, and partition chromatography. In affinity chromatography, a solid phase adsorbent contains groups that bind particular proteins because they resemble ligands for which the proteins have a natural affinity. In a preferred mode, the solid phase adsorbent contains one or more FAAH inhibitors which bind the enzyme. In antibody affinity chromatography, a solid phase immunoabsorbent having antibodies with a bind specificity with respect to FAAH are employed. In electric chromatography or electrophoresis, the FAAH is separated from other molecules according to its molecular weight or isoelectric point. In gel filtration, also known as gel permeation, molecular sieve, and exclusion chromatography, the solid phase creates a stationary phase of gel solvent and a mobile phase of excluded solvent. The FAAH is separated according to its molecular size as it partitions between the stationary and mobile phases. The gel particles are selected to have a exclusion size in excess of FAAH. In ion exchange chromatography, a solid phase ion exchanger is employed for separating the FAAH from other molecules according to its partitioning between ionic and nonionic forces. In partition chromatography, immiscible fluids having a stationary and mobile phases are employed for separating the FAAH according to its partitioning between the two immiscible phases. Preferred chromatographic methodologies include DEAE chromatography, affinity chromatography on a solid phase having attached Hg groups derivatized with an inhibitor of FAAH such as a trifluoroketone.
In a preferred mode, a crude source of FAAH is purified in four steps. In the first step, a crude source of FAAH is purified by exchange chromatography using a DEAE chromatography column to form a first elution product. In the second step, the elution product from the first step is further purified by partitioning by with affinity chromatography to form a second elution product. In the third step, elution product from the second step is further purified by partitioning with Heparin affinity chromatography to form a third elution product. In the fourth step, the elution product from the third step is further purified by partitioning with an stationary phase derivatized with a trifluoroketone inhibitor of FAAH. The eluant from the fourth step form the purified form of FAAH.
FAAH can be isolated from any of a variety of mammalian species, including rat, mouse or human, as described herein.
Fatty-acid amid hydrolase (FAAH) is characterized by inclusion of an amino acid sequence selected from a group consisting of:
Another aspect of the invention is directed to a method for catalyzing the hydrolysis of a fatty acid primary amide. In this hydrolysis method, the fatty acid primary amide is combined or contacted with a catalytic amount of purified form of FAAH. In a preferred mode, the fatty acid primary amide is of a type which includes an alkyl chain having an unsaturation or more particularly is represented by the following formula:
NH2C(O)(CH2)(6xe2x89xa7nxe2x89xa611)CHxe2x95x90CH(CH2)(8xe2x89xa7nxe2x89xa65)CH3. 
More particularly, the unsaturation of the alkyl chain may have a cis configuration or may be identically cis-9,10-octadecenoamide, cis-8,9-octadecenoamide, cis-11,12-octadecenoamide, or cis-13,14-docosenoamide.
Another aspect of the invention is directed to a method for inhibiting an enzymatically catalyzed hydrolysis of fatty acid primary amides, such as cis-9,10-octadecenoamide, by FAAH. In this method, FAAH is combined or contacted with an inhibitor of FAAH. Preferred inhibitors include phenylmethylsulfonyl fluoride, HgCl2, and a trifluoroketone having the following structure: 
Another aspect of the invention is directed to a method for ascertaining the inhibitory activity of a candidate inhibitor of FAAH. Thus, FAAH is admixed with a candidate FAAH inhibitor to assess inhibitory capacity in a screening method.
In a preferred method for determining inhibitory activity of a candidate FAAH inhibitor, the contemplated method comprises five steps. In the first step, a mixture xe2x80x9cAxe2x80x9d is formed by combining FAAH and cis-9,10-octadecenoamide substrate under reaction conditions. In the second step, a mixture xe2x80x9cBxe2x80x9d is formed by combining the mixture xe2x80x9cAxe2x80x9d with the candidate inhibitor. In the third step, the conversion of cis-9,10-octadecenoamide substrate to a hydrolysis product within mixture xe2x80x9cAxe2x80x9d is quantified. In the fourth step, the conversion of cis-9,10-octadecenoamide substrate to hydrolysis product within mixture xe2x80x9cBxe2x80x9d is quantified. In the fifth step, the inhibitory activity of the candidate inhibitor is ascertained by comparing the quantifications of steps three and four.
Another aspect of the invention is directed to a trifluoroketone inhibitor of FAAH represented by following structure: 
Another aspect of the invention is directed to one or more nucleotide sequences the encode part or all of FAAH. The complete nucleotide sequence that encodes human, mouse or rat FAAH are shown in SEQ ID Nos. 42, 39 or 35, respectively.
The partial nucleotide sequence of rat FAAH is represented as follows: